Even though the automotive industry has over the years, if for no other reason than seeking competitive advantages, continually exerted efforts to increase the fuel economy of automotive engines, the gains continually realized thereby have been deemed by various levels of government as being insufficient. Further, such levels of government have also arbitrarily imposed regulations specifying the maximum permissible amounts of carbon monoxide (CO), hydrocarbons (HC) and oxides of nitrogen (NO.sub.x) which may be emitted by the engine exhaust gases into the atmosphere.
Unfortunately, generally, the available technology employable in attempting to attain increases in engine fuel economy is contrary to that technology employable in attempting to meet the governmentally imposed standards on exhaust emissions.
For example, the prior art in trying to meet the standards for NO.sub.x emissions has employed a system of exhaust gas recirculation whereby at least a portion of the exhaust gas in reintroduced into the cylinder combustion chamber to thereby lower the combustion temperature therein and consequently reduce the formation of NO.sub.x.
The prior art has also proposed the use of engine crankcase recirculation means whereby the vapors which might otherwise become vented to the atmosphere are introduced into the engine combustion chambers for further burning.
The prior art has also proposed the use of fuel metering means which are effective for metering a relatively overly rich (in terms of fuel) fuel-air mixture to the engine combustion chamber means as to thereby reduce the creation of NO.sub.x within the combustion chamber. The use of such overly rich fuel-air mixtures results in a substantial increase in CO and HC in the engine exhaust which, in turn, requires the supplying of additional oxygen, as by an associated air pump, to such engine exhaust in order to complete the oxidation of the CO and HC prior to its delivery into the atmosphere.
The prior art has also heretofore proposed employing the retarding of the engine ignition timing as a further means for reducing the creation of NO.sub.x. Also, lower engine compression ratios have been employed in order to lower the resulting combustion temperature within the engine combustion chamber and thereby reduce the creation of NO.sub.x. In this connection the prior art has employed what is generally known as a dual bed catalyst. That is, a chemically reducing first catalyst is situated in the stream of exhaust gases at a location generally nearer the engine while a chemically oxidizing second catalyst is situated in the stream of exhaust gases at a location generally further away from the engine and downstream of the first catalyst. The relatively high concentrations of CO resulting from the overly rich fuel-air mixtures are used as the reducing agent for NO.sub.x in the first catalyst while extra air supplied (as by an associated pump) to the stream of exhaust gases, at a location generally between the two catalysts, serves as the oxidizing agent in the second catalyst. Such systems have been found to have various objections in that, for example, they are comparatively very costly requiring additional conduitry, air pump means and an extra catalyst bed. Further, in such systems, there is a tendency to form ammonia which, in turn, may or may not be reconverted to NO.sub.x in the oxidizing catalyst bed.
The prior art has also proposed the use of fuel metering injection means for eliminating the usually employed carbureting apparatus and, under superatmospheric pressure, injecting the fuel through individual nozzles directly into the respective cylinders of a piston type internal combustion engine. Such fuel injection systems, besides being costly, have not proven to be generally successful in that the system is required to provide metered fuel flow over a very wide range of metered fuel flows. Generally, those prior art injection systems which are very accurate at one end of the required range of metered fuel flows, are relatively inaccurate at the opposite end of that same range of metered fuel flows. Also, those prior art injection systems which are made to be accurate in the mid-portion of the required range of metered fuel flows are usually relatively inaccurate at both ends of that same range. The use of feedback means for altering the metering characteristics of such prior art fuel injection systems has not solved the problem of inaccurate metering because the problem usually is intertwined within such factors as: effective aperture area of the injector nozzle; comparative movement required by the associated nozzle pintle or valving member; inertia of the nozzle valving member; and nozzle "cracking" pressure (that being the pressure at which the nozzle opens). As should be apparent, the smaller the rate of metered fuel flow desired, the greater becomes the influence of such factors thereon.
It is now anticipated that the said various levels of government will be establishing even more stringent exhaust emission limits.
The prior art, in view of such anticipated requirements, with respect to NO.sub.x, has suggested the employment of a "three-way" catalyst, in a single bed, within the stream of exhaust gases as a means of attaining such anticipated exhaust emission limits. Generally, a "three-way" catalyst is a single catalyst, or catalyst mixture, which catalyzes the oxidation of hydrocarbons and carbon monoxide and also the reduction of oxides of nitrogen. It has been discovered that a difficulty with such a "three-way" catalyst system is that if the fuel metering is too rich (in terms of fuel) the NO.sub.x will be reduced effectively but the oxidation of CO will be incomplete; if the fuel metering is too lean, the CO will be effectively oxidized but the reduction of NO.sub.x will be incomplete. Obviously, in order to make such a "three-way" catalyst system operative, it is necessary to have very accurate control over the fuel metering function of the associated fuel metering supply means feeding the engine. As hereinbefore described, the prior art has suggested the use of fuel injection means, employing respective nozzles for each engine combustion chamber, with associated feedback means (responsive to selected indicia of engine operating conditions and parameters) intended to continuously alter or modify the metering characteristics of the fuel injection means. However, as also hereinbefore indicated, such fuel injection systems have not proven to be successful.
It has also heretofore been proposed to employ fuel metering means, of a carbureting type, with feedback means responsive to the presence of selected constituents comprising the engine exhaust gases. Such feedback means were employed to modify the action of a main metering rod of a main fuel metering system of a carburetor. However, tests and experience have indicated that such a prior art carburetor and such a related feedback means can never provide the degree of accuracy required in the metering of fuel to an associated engine as to assure meeting, for example, the said anticipated exhaust emission standards.
Further, various prior art structures have experienced problems in being able to supply metered fuel, at either a proper rate or in a proper manner, as to provide for a smooth engine and/or vehicle acceleration when such is demanded.
The prior art has proposed many specific forms of fuel metering arrangements employable in either or both of such overall systems generally classified as fuel "injection systems" or "carbureting systems".
Regardless of the overall system in which employed, such prior art fuel metering arrangements can be grouped into two general catagories. The first of such catagories comprises those metering arrangements wherein a valving member is partly or wholly received within a cooperating metering orifice and axially movable relative to such orifice in order to thereby vary the effective flow area of the metering orifice and thereby variably control the rate of metered fuel flow through the orifice for a given pressure differential thereacross. The valving element 69 and/or 72 and cooperating orifice 20 of U.S. Pat. No. 4,217,314 as well as valving member 140 and orifice 144 of U.S. Pat. No. 4,246,875 may be considered as generally typifying such first catagory of prior art metering arrangements.
The second of such catagories comprises a valving arrangement whereby a valve member is oscillatingly or intermittently moved as to alternatingly close and open an associated metering orifice or passage.
In such a prior art metering arrangement the ratio of the cycle time during which the valve member is positioned as to have the associated metering orifice or passage open compared to the cycle time during which the valve member is positioned as to have the associated metering orifice or passage closed determines the rate of metered fuel flow through such metering orifice or passage. The valving member 227 and cooperating orifice or passage 171 of U.S. Pat. No. 4,294,282 as well as the valving member 74 and cooperating orifice or passage 72 of U.S. Pat. No. 4,406,266 may be considered as generally typifying such second catagory of prior art metering arrangements.
In said first catagory, the dimensions of both the valve member and cooperating orifice must be held to very close tolerances and there are additional problems of maintaining concentricity not only in the respective valve member and cooperating orifice but also as between the two even during axial movement of the valve member. Further, as vehicular engines become smaller the rates of metered fuel flow to the engine also become lesser and the problems of close tolerances, concentricity and alignment of and between the valve member and cooperating orifice are exacerbated because the effective flow or metering area is reduced and what might have been previously acceptable as a dimensional tolerance or variation becomes, precentage-wise, to great to tolerate in a metering area of considerably reduced magnitude. Such reduced areas are also highly susceptible to becoming either partly or completely clogged by foreign particles entrained in the fuel.
In said second catagory, the valve member may be oscillated (to and from a closed position), for example, at a rate of 80 cycles per second. (Some prior art systems employ a slower rate while others employ even a faster rate.) Such prior art metering arrangements depend on achieving a total termination of fuel flow during the time that the valve member is moved to a closed position against the cooperating fuel metering orifice or passage. However, this is difficult to achieve because of the tendency of the valving member to bounce back away from its seat or because of the wear experienced by the valve member during normal operation with such wear producing fuel leakage paths past the valve member. Attempts to solve such problems as by the use of, for example, a ball valve member and cooperating generally conical seat have not, thus far, produced appreciable benefits.
Accordingly, the invention as disclosed and described is directed, primarily to the solution of such and other related and attendant problems of the prior art.